This application is related to Japanese Patent Application No. H11-238783, filed on Aug. 25, 1999, the disclosure of which is hereby incorporated by reference in its entirety.
The present invention relates to a pretensioner that is built into a seatbelt device for restraining passengers to the seats of vehicles and the like, for rotating the take-up shaft for a seatbelt in the take-up direction in an emergency. More particularly, the present invention relates to a pretensioner with improved safety, wherein gas is allowed to escape appropriately in the event that the internal gas pressure rises excessively and there are decreased adverse effects on other equipment.
In recent years, an increasing number of seatbelt devices with pretensioners have been provided to vehicles, principally automobiles. A pretensioner is for instantaneously rotating the reel (take-up shaft) on which the seatbelt is wound in the take-up direction in the event of a vehicle collision, thereby taking up the slack in the belt and providing the belt with tension. The device driving this pretensioner generally ignites gunpowder according to a detection signal emitted at the time of collision of the vehicle and drives a reel rotating mechanism by gas pressure generated by the explosion of gunpowder. A conventional example of such a pretensioner is the pretensioner disclosed in U.S. Pat. No. 5,875,634, for example. FIG. 9(A) is a perspective view illustrating the configuration of the pipe base portion of the above pretensioner, and FIG. 9(B) is a frontal cross-section view of the same part, and FIG. 9(C) is a frontal cross-section view in the event that abnormal pressure is applied within the pipe.
This pretensioner has a pipe 110. A ball 116 is stored within this pipe 110. An attachment portion 111 is formed at the end portion of the pipe 110. This attachment portion 111 is formed so as to be somewhat greater in diameter than the pipe 110. A sleeve 114 is fixed at the inner side of the attachment portion 111. A gas generator 113 is stored within the sleeve 114. Further, a hole 115 is formed to the side wall of the attachment portion 111.
The gas generator 113 explodes in response to the signal at the time of collision of the vehicle, and discharges high-pressure gas within the pipe 110. The ball 116 is accelerated by the energy of this gas. Following moving through the pipe 110, the accelerated ball 116 drives the driving belt take-up mechanism. Now, in the event that abnormal pressure exceeding normal operating pressure occurs within the pipe 110, the portion within the hole 115 bursts as shown in FIG. 9(C), and the gas generator 113 gas blows out from here. Thus, dangerously high pressure can be prevented from occurring within the pipe 110.
However, with the above conventional pretensioner, at the time of abnormal pressure exceeding normal operating pressure occurring within the pipe 110 and the inner side of the hole 115 bursting, debris from the broken portion flies. There has been the possibility that this debris could have adverse effects on other equipment in the pretensioner.
The present invention has been made in light of the above problems, and it is an object thereof to provide a pretensioner with improved safety, wherein gas is allowed to escape appropriately in the event that the internal gas pressure rises excessively, and there are no adverse effects on other equipment.
In order to solve the above problems, the pretensioner according to the present invention is a pretensioner for rotating the take-up shaft of a seatbelt in the take-up direction in the event of an emergency to provide the belt with pretension, comprising: a gas generator; a driving member accelerated by the gas generated by the gas generator; a path for storing and guiding the driving member; a channel for guiding the gas to the path; means for converting the motion of the accelerated driving member into force for rotating the take-up shaft; wherein, in the event that internal pressure exceeding a certain pressure (i.e., abnormal pressure) is applied to the channel, a gas escaping hole opens in the driving means, thereby discharging gas from the channel to the path beyond the driving member.
With such a pretensioner, even in the event that internal pressure exceeding a certain pressure (i.e., abnormal pressure) is applied to the channel, a gas releasing hole opens in the driving member due to this abnormal pressures, so the gas escapes to the driving member path beyond the driving member from this hole. Accordingly, trouble such as the channel being damaged by the abnormal pressure can be lessened.
Not only that, the gas is discharged into the path, so debris from the material does not fly in the direction of other equipment as with conventional arrangements. Accordingly, adverse effects of debris on equipment other than the pretensioner such as the seatbelt retractor can be avoided.
With the pretensioner according to the present invention, the driving member may comprise a resin member positioned on the side of the gas generator, and a metal member adjacent to the resin member; wherein a gas releasing piston formed of a material harder than the resin member is enveloped within both members; and wherein in the event that internal pressure exceeding a certain pressure (i.e., abnormal pressure) is applied to the channel, the resin member tears and gas passes between the gas releasing piston and the metal member and is discharged from the channel to the path.
Also, with the pretensioner according to the present invention, the gas releasing piston may comprise a material having a through hole. Accordingly, in the event that internal pressure exceeding a certain pressure (i.e., abnormal pressure) is applied to the channel, the resin member tears and gas passes through the through hole in the gas releasing piston and is discharged from the channel to the path.
The present invention is directed to overcoming or at least reducing some of the problems set forth above and is directed to accomplishing at least some of the objectives set forth above.